1. Field of the Invention
The present invention relates to an apparatus for applying an x-ray source, for radiation therapy port verification. More particularly, the present invention relates to an apparatus for taking high quality images of radiotherapy treatments to confirm the accuracy of those treatments.
2. Description of the Prior Art
U.S. Pat. No. 5,165,093 (Miller et al), assigned to The Titan Corporation, discloses an interstitial X-ray needle which is intended to deliver radiation and to treat tumors. One end of an elongated X-ray tube is coupled to an electron emitter and a converter element is disposed at the tip of the other end of the tube to convert electrons into X-rays. A solenoid coil is wound around the tube to provide a magnetic field to confine the electrons within a narrow beam. The tube and the coil are encased in an elongated outer casing, and a pipe is coaxially disposed between the casing and the tube thereby defining an inner annular flow chamber between the tip of the tube and the coolant inlet in the casing and an outer annular flow chamber between the tip of the tube and a coolant outlet in the casing.
The x-ray needle according to Miller et al has a diameter small enough so that it can be inserted into a patient without causing significant damage to the tissue between the skin and the tumor site, an increasing the applicability of x-ray therapy for the treatment of cancerous internal body parts. By winding the solenoid coil around the beam transport tube and thereby providing a magnetic field that tightly confines the emitted electrons, electron loss and stray x-radiation is prevented. However, the Miller et al. device as tested suffered from problems related to focusing the electron beam on the target, insufficient output and target design.
U.S. Pat. No. 5,471,516 (to Nunan), and assigned to Varian Associates, Inc., teaches a radiotherapy apparatus equipped with a low dosage localizing and portal imaging x-ray source. The device disclosed in the Nunan patent incorporates an x-ray source inside the treatment head of an accelerator to achieve positioning of a low energy x-ray source coincident with a high energy x-ray source.
Portal films or electronic portal imaging systems are used to verify tumor positioning. Megavolt therapeutic x-rays emerging from the patient are used to generate the images. Unfortunately, the images are of inherently low contrast and poor quality.
The patent to Fenn (U.S. Pat. No. 5,737,384) discloses an x-ray needle providing heating with microwave energy. Both the Fenn and Miller et al. patents are intended to be used interstitially to deliver radiation and heat to treat tumors and were not intended for imaging purposes.
The Nunan patent is mainly concerned with the retractable target, and, in particular, as it relates to the application of low energy x-rays. The apparatus set forth in the Nunan patent does not provide adequate focusing which causes decreased output and creates stray sources of x-rays in the head. Additionally, the Nunan apparatus locates the entire generating device inside the head of the machine, and it is not capable of variable energies. In order to achieve optimum diagnostic images, it is essential to have control over the electron energies being used to generate the x-ray beam.